1. Field of the Invention
This invention relates to holography, three-dimensional imaging, integral holography or multiplexed holography, and more particularly, to full-color holography.
2. Description of the Prior Art
Several methods of making full-color holograms have been demonstrated in the past, all of which are adequately summarized in "Optical Holography," by Collier, Burkhardt and Lin. These prior methods may be classified into three groups.
The first group represents the methods which rely on superimposing three holograms exposed with different colors on a single undivided holographic plate using identical reference beam angles. In a thin recording medium, this approach is not effective unless the viewing angle (the viewing aperture) is severely restricted. In a thick medium, the approach works very well for reasonably shallow scenes, particularly for reflection holograms. The problem with this approach is that volume recording materials are too expensive for many potential applications of holography.
The second group represents the methods which rely on different reference beam angles for three-color component holograms superimposed on the same holographic plate. This approach has been applied to "Benton-type" or "rainbow" holograms, thereby providing white light viewable holograms that appear to be in full color when viewed through a narrow aperture. When viewed outside the narrow aperture, the color ceases to appear realistic; furthermore, Benton-type holograms have a very limited vertical field of view.
The third group represents methods which depend on spatial sampling. As stated in "Optical Holography":
If the hologram is recorded as a composite of many small areas, each of which records holographic fringes formed with one wavelength only, false reconstruction and false images can be eliminated entirely. A random distribution of these areas of elements is preferable, but an interlaced sequence, ordered according to wavelength, is permissible if the elements are small. In the reconstruction step, each element must be illuminated only by light of the wavelength used to form it. There then can be no crossmodulation and no false images. Each wavelength component of the subject wave is reconstructed from discrete noncontiguous samples of hologram area. Resolution is sacrificed in the process.
The third group of methods has been directed only toward "classical holograms"; i.e., holograms containing both horizontal and vertical parallax which are only viewable in monochromatic light. If the methods were directly applied to Benton-type holograms, no advantage would result, because the viewing aperture would be as limited as it is with the "second group methods" described above. However, the "third group methods" have never been tried on Benton-type holograms.
None of the ways heretofore proposed or demonstrated for generating full-color holograms are capable of generating holograms that are simultaneously free of color cross talk, white light viewable, and capable of displaying deep, clear images viewable through a large viewing aperture. In addition, none of the ways previously described or demonstrated is readily adaptable to inexpensive, high-volume hologram replication techniques, such as thermoforming.